enzymes- lqc 8a Flashcards
biological catalyst
A molecule produced by an {organism/cell}, which speeds up the rate of a biological reaction by reducing the activation energy and is not used up in the reaction;
activation energy
Energy needed for a reaction to occur, by causing bonds to {break / form} and which is reduced by enzymes ;
Structure of an enzyme
An enzyme is a globular protein, so has tertiary structure held together by ionic, hydrogen and disulphide bonds between R groups, giving it a spherical shape. An enzyme also has hydrophilic amino acids on the outside and hydrophobic amino acids on the inside. An enzyme also has an active site , which is a specific shape to fit the shape of a specific substrate.
step 1 of a mechanism of enzyme action
The substrate fits into and binds to the enzyme active site
step 2 of a mechanism of enzyme action
The shape of the active site fits the shape of the substrate – lock and key theory or induced fit theory
step 3 of a mechanism of enzyme action
An enzyme-substrate complex forms and the substrate is held in the correct position for bonds to be broken or formed, and product to be made. This lowers the activation energy for the reaction.
step 4 of a mechanism of enzyme action
The product is released from the active site and the enzyme is unchanged/not used up and is therefore free to accept another substrate molecule
Explain why an enzyme can only catalyse one reaction (has one substrate).
- Enzyme has a {specific tertiary structure/ is specific/ has a specific substrate} ;
- Due to the specific shape of active site;
- Only the substrate will fit into the active site / explanation of ‘lock and key’, where enzyme is lock and substrate is the key;
- To form an enzyme-substrate complex;
- Another substrate has a different shape;
Distinguish between an intracellular enzyme and an extracellular enzyme.
Intracellular enzymes catalyse reactions inside cells, but extracellular enzymes catalyse reactions outside cells
